Re: LF: Ferrite antennas

[Daniele Tincani <danieletincani@yahoo.com>]

Hello Mike, LF,

 

I'm waiting from ferrites and litz wire to arrive from eBay, then I will be able to start my experiments for a wideband ferrite-cored antenna covering as much as possible of LF. Major uncertainties for me are on the mechanical construction, I mean: inner shielding (between the rod and the coil) vs. outer shielding; compact winding vs. longer coil (how long?); leaving some space between the coil and the core or not; etc..

As there are so many design parameters to consider, I would like to fix some at least. So I plan to start with inner shielding only - made by slotted aluminium tube (outer shield can be added later for test); compact winding (should be OK with litz); piece of PVC tube used both as a spacer (between the rod and the coil) and a isolating mechanical support for 2-3 stacked rods (20cm each) in further tests.

I would like to know if anyone on the LF reflector has comments/results about using a plastic spacer (e.g. PVC tube) between the core and the coil. The tube is 16mm outer diameter, while the ferrites are 10mm. If there are not real advantages in having more space between the rod and the coil, then I think the aluminium tube used for inner shielding could be sufficient also as the mechanical support for winding.

 

Best regards

Daniele

 

Da: Mike Dennison <mike.dennison@ntlworld.com>
A: rsgb_lf_group@blacksheep.org
Inviato: Lunedì 12 Settembre 2011 14:36
Oggetto: LF: Ferrite antennas

I have been following the discussion on ferrite receiving antennas -
due to work pressures I am a few weeks behind in reading the mail.

The use of this type of antenna for LF amateur radio is not new. I
used it successfully as a portable antenna on the old 73kHz band
several years ago.

I used the existing winding (LItz) an ordinary long-wave broadcast
radio antenna. The rod was about 150mm long. The coil, tuned with a
large fixed C and a variable C, formed the drain load of a 2N3819,
with the output taken from the source. The selectivity was very high
indeed (essential to reduce the huge commercial signal on the 73kHz
band) and sensitivity was adequate to overcome the noise level of my
very sensitive Datong LF converter.

The interesting thing was that Peter, G3LDO, tried to replicate this
and had poorer results, perhaps indicating that not all long wave
radios had ferrite that worked at 73kHz.

Mike, G3XDV
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